WO 03/080872 A1 discloses a chromatographic separation process for separating sugars, sugar alcohols, other carbohydrates and mixtures thereof from plant-based solutions as well as the separation of sugars and sugar alcohols from each other with weak base anion exchange resins. The plant-based solutions used as the feed in the separation may be biomass hydrolysates, molasses and vinasse solutions and process streams like xylose, sucrose, glucose and fructose streams, for example. It is recited that a weak acid cation exchange resin and/or a strong acid cation exchange resin may also be used in the chromatographic separation. The examples of said document show good separation of rhamnose and the recovery of rhamnose-enriched fractions with weak base anion exchange resins. It is also recited in the examples that said resin separates glycerol and inositol from betaine and maltose from glucose, for example. The examples of said document do not disclose the recovery xylose-enriched fractions with weak base anion exchange resins.
US 2008/0041366 A1 discloses a process for separating organic acids and/or salts thereof from an aqueous sugar stream by passing the stream through one or more beds of anion exchange resins. The sugar stream may be a hydrolysate of lignocellulosic feedstock, comprising sugars selected from xylose, glucose, arabinose, galactose, mannose and combinations thereof. The anion exchange resin may be a weak base anion exchange resin. One or more product streams comprising organic acids and/or salts thereof are recovered. Furthermore, a sugar stream substantially free of mineral acids and organic acids is obtained.
WO 02/27038 A1 discloses the use of a weak acid cation exchange resin for chromatographic separation of carbohydrates, especially for the separation of hydrophobic saccharides, such as deoxy, methyl and anhydro sugars and anhydrosugar alcohols from more hydrophilic saccharides. The feeds for the separation may be for example xylose, sucrose, starch or maltose process streams. The examples show good separation of rhamnose, separation of sucrose from monosaccharides, separation of fructose from oligosaccharides, and the separation of sodium chloride, betaine, erythritol and inositol, for example.
WO 02/27039 A1 discloses a method for recovering a monosaccharide selected from rhamnose, arabinose, xylose and mixtures thereof from feeds such as hemicellulose hydrolysates by a multistep chromatographic process, where a weak acid cation exchange resin is used in at least one step of the multistep process. It is recited that a strong acid cation exchange resin may also be used in the separation. The examples show good separation of rhamnose with weak acid cation exchange resins. The examples also show the separation of xylose with strong acid cation exchange resins.
Furthermore, the separation of xylose with strong acid cation exchange resins is disclosed for example in U.S. Pat. No. 4,075,406, WO 97/49658 and U.S. Pat. No. 5,998,607. U.S. Pat. No. 4,075,406 discloses the separation of xylose from xylan-containing raw material, such as birch wood, corn cobs and cotton seed hulls. WO 97/49658 discloses the separation of xylose and xylonic acid from Mg-sulphite cooking liquor, whereafter the fraction containing xylose and xylonic acid is subjected to reduction to obtain xylitol. U.S. Pat. No. 5,998,607 also discloses the separation of xylose together with xylonic acid from a sulphite cooking liquor, followed by the separation of xylose and xylonic acid from each other and reduction thereof to xylitol.
However, the methods described above, such as those based on the use of strong acid action exchange resins, have not always provided xylose with the required yields and purities. Consequently, there is still need for improved xylose recovery methods.